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<title>Overview of the Criteria and Metamodel APIs - The Java EE 6 Tutorial</title>
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      <td width="400px"><p class="toc level1"><a href="docinfo.html">Document Information</a></p>
<p class="toc level1 tocsp"><a href="gexaf.html">Preface</a></p>
<p class="toc level1 tocsp"><a href="gfirp.html">Part&nbsp;I&nbsp;Introduction</a></p>
<p class="toc level2"><a href="bnaaw.html">1.&nbsp;&nbsp;Overview</a></p>
<p class="toc level2"><a href="gfiud.html">2.&nbsp;&nbsp;Using the Tutorial Examples</a></p>
<p class="toc level1 tocsp"><a href="bnadp.html">Part&nbsp;II&nbsp;The Web Tier</a></p>
<p class="toc level2"><a href="bnadr.html">3.&nbsp;&nbsp;Getting Started with Web Applications</a></p>
<p class="toc level2"><a href="bnaph.html">4.&nbsp;&nbsp;JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="giepx.html">5.&nbsp;&nbsp;Introduction to Facelets</a></p>
<p class="toc level2"><a href="gjddd.html">6.&nbsp;&nbsp;Expression Language</a></p>
<p class="toc level2"><a href="bnaqz.html">7.&nbsp;&nbsp;Using JavaServer Faces Technology in Web Pages</a></p>
<p class="toc level2"><a href="gjcut.html">8.&nbsp;&nbsp;Using Converters, Listeners, and Validators</a></p>
<p class="toc level2"><a href="bnatx.html">9.&nbsp;&nbsp;Developing with JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="gkmaa.html">10.&nbsp;&nbsp;JavaServer Faces Technology Advanced Concepts</a></p>
<p class="toc level2"><a href="bnawo.html">11.&nbsp;&nbsp;Configuring JavaServer Faces Applications</a></p>
<p class="toc level2"><a href="gkiow.html">12.&nbsp;&nbsp;Using Ajax with JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="gkhxa.html">13.&nbsp;&nbsp;Advanced Composite Components</a></p>
<p class="toc level2"><a href="bnavg.html">14.&nbsp;&nbsp;Creating Custom UI Components</a></p>
<p class="toc level2"><a href="bnafd.html">15.&nbsp;&nbsp;Java Servlet Technology</a></p>
<p class="toc level2"><a href="bnaxu.html">16.&nbsp;&nbsp;Internationalizing and Localizing Web Applications</a></p>
<p class="toc level1 tocsp"><a href="bnayk.html">Part&nbsp;III&nbsp;Web Services</a></p>
<p class="toc level2"><a href="gijti.html">17.&nbsp;&nbsp;Introduction to Web Services</a></p>
<p class="toc level2"><a href="bnayl.html">18.&nbsp;&nbsp;Building Web Services with JAX-WS</a></p>
<p class="toc level2"><a href="giepu.html">19.&nbsp;&nbsp;Building RESTful Web Services with JAX-RS</a></p>
<p class="toc level2"><a href="gjjxe.html">20.&nbsp;&nbsp;Advanced JAX-RS Features</a></p>
<p class="toc level2"><a href="gkojl.html">21.&nbsp;&nbsp;Running the Advanced JAX-RS Example Application</a></p>
<p class="toc level1 tocsp"><a href="bnblr.html">Part&nbsp;IV&nbsp;Enterprise Beans</a></p>
<p class="toc level2"><a href="gijsz.html">22.&nbsp;&nbsp;Enterprise Beans</a></p>
<p class="toc level2"><a href="gijre.html">23.&nbsp;&nbsp;Getting Started with Enterprise Beans</a></p>
<p class="toc level2"><a href="gijrb.html">24.&nbsp;&nbsp;Running the Enterprise Bean Examples</a></p>
<p class="toc level2"><a href="bnbpk.html">25.&nbsp;&nbsp;A Message-Driven Bean Example</a></p>
<p class="toc level2"><a href="gkcqz.html">26.&nbsp;&nbsp;Using the Embedded Enterprise Bean Container</a></p>
<p class="toc level2"><a href="gkidz.html">27.&nbsp;&nbsp;Using Asynchronous Method Invocation in Session Beans</a></p>
<p class="toc level1 tocsp"><a href="gjbnr.html">Part&nbsp;V&nbsp;Contexts and Dependency Injection for the Java EE Platform</a></p>
<p class="toc level2"><a href="giwhb.html">28.&nbsp;&nbsp;Introduction to Contexts and Dependency Injection for the Java EE Platform</a></p>
<p class="toc level2"><a href="gjbls.html">29.&nbsp;&nbsp;Running the Basic Contexts and Dependency Injection Examples</a></p>
<p class="toc level2"><a href="gjehi.html">30.&nbsp;&nbsp;Contexts and Dependency Injection for the Java EE Platform: Advanced Topics</a></p>
<p class="toc level2"><a href="gkhre.html">31.&nbsp;&nbsp;Running the Advanced Contexts and Dependency Injection Examples</a></p>
<p class="toc level1 tocsp"><a href="bnbpy.html">Part&nbsp;VI&nbsp;Persistence</a></p>
<p class="toc level2"><a href="bnbpz.html">32.&nbsp;&nbsp;Introduction to the Java Persistence API</a></p>
<p class="toc level2"><a href="gijst.html">33.&nbsp;&nbsp;Running the Persistence Examples</a></p>
<p class="toc level2"><a href="bnbtg.html">34.&nbsp;&nbsp;The Java Persistence Query Language</a></p>
<p class="toc level2"><a href="gjitv.html">35.&nbsp;&nbsp;Using the Criteria API to Create Queries</a></p>
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<p class="toc level3"><a href="">Overview of the Criteria and Metamodel APIs</a></p>
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<p class="toc level3"><a href="gjiup.html">Using the Metamodel API to Model Entity Classes</a></p>
<p class="toc level4"><a href="gjiup.html#gjivl">Using Metamodel Classes</a></p>
<p class="toc level3 tocsp"><a href="gjivm.html">Using the Criteria API and Metamodel API to Create Basic Typesafe Queries</a></p>
<p class="toc level4"><a href="gjivm.html#gjivs">Creating a Criteria Query</a></p>
<p class="toc level4"><a href="gjivm.html#gjivq">Query Roots</a></p>
<p class="toc level4"><a href="gjivm.html#gjiuv">Querying Relationships Using Joins</a></p>
<p class="toc level4"><a href="gjivm.html#gjive">Path Navigation in Criteria Queries</a></p>
<p class="toc level4"><a href="gjivm.html#gjivi">Restricting Criteria Query Results</a></p>
<p class="toc level5"><a href="gjivm.html#gjiwn">The <tt>Expression</tt> Interface Methods</a></p>
<p class="toc level5"><a href="gjivm.html#gjixa">Expression Methods in the <tt>CriteriaBuilder</tt> Interface</a></p>
<p class="toc level4 tocsp"><a href="gjivm.html#gjixe">Managing Criteria Query Results</a></p>
<p class="toc level5"><a href="gjivm.html#gjiwo">Ordering Results</a></p>
<p class="toc level5"><a href="gjivm.html#gjixg">Grouping Results</a></p>
<p class="toc level4 tocsp"><a href="gjivm.html#gjivy">Executing Queries</a></p>
<p class="toc level5"><a href="gjivm.html#gjiur">Single-Valued Query Results</a></p>
<p class="toc level5"><a href="gjivm.html#gjivp">Collection-Valued Query Results</a></p>
<p class="toc level2 tocsp"><a href="gkjiq.html">36.&nbsp;&nbsp;Creating and Using String-Based Criteria Queries</a></p>
<p class="toc level2"><a href="gkjjf.html">37.&nbsp;&nbsp;Controlling Concurrent Access to Entity Data with Locking</a></p>
<p class="toc level2"><a href="gkjia.html">38.&nbsp;&nbsp;Improving the Performance of Java Persistence API Applications By Setting a Second-Level Cache</a></p>
<p class="toc level1 tocsp"><a href="gijrp.html">Part&nbsp;VII&nbsp;Security</a></p>
<p class="toc level2"><a href="bnbwj.html">39.&nbsp;&nbsp;Introduction to Security in the Java EE Platform</a></p>
<p class="toc level2"><a href="bncas.html">40.&nbsp;&nbsp;Getting Started Securing Web Applications</a></p>
<p class="toc level2"><a href="bnbyk.html">41.&nbsp;&nbsp;Getting Started Securing Enterprise Applications</a></p>
<p class="toc level1 tocsp"><a href="gijue.html">Part&nbsp;VIII&nbsp;Java EE Supporting Technologies</a></p>
<p class="toc level2"><a href="gijto.html">42.&nbsp;&nbsp;Introduction to Java EE Supporting Technologies</a></p>
<p class="toc level2"><a href="bncih.html">43.&nbsp;&nbsp;Transactions</a></p>
<p class="toc level2"><a href="bncjh.html">44.&nbsp;&nbsp;Resource Connections</a></p>
<p class="toc level2"><a href="bncdq.html">45.&nbsp;&nbsp;Java Message Service Concepts</a></p>
<p class="toc level2"><a href="bncgv.html">46.&nbsp;&nbsp;Java Message Service Examples</a></p>
<p class="toc level2"><a href="gkahp.html">47.&nbsp;&nbsp;Advanced Bean Validation Concepts and Examples</a></p>
<p class="toc level2"><a href="gkeed.html">48.&nbsp;&nbsp;Using Java EE Interceptors</a></p>
<p class="toc level1 tocsp"><a href="gkgjw.html">Part&nbsp;IX&nbsp;Case Studies</a></p>
<p class="toc level2"><a href="gkaee.html">49.&nbsp;&nbsp;Duke's Tutoring Case Study Example</a></p>
<p class="toc level1 tocsp"><a href="idx-1.html">Index</a></p>
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<a name="gjrij"></a><h2>Overview of the Criteria and Metamodel APIs</h2>
<a name="indexterm-1870"></a><p>Similar to JPQL, the Criteria API is based on the abstract schema
of persistent entities, their relationships, and embedded objects. The Criteria API operates on this
abstract schema to allow developers to find, modify, and delete persistent entities by
invoking Java Persistence API entity operations. The Metamodel API works in concert with
the Criteria API to model persistent entity classes for Criteria queries.</p>

<p>The Criteria API and JPQL are closely related and are designed to
allow similar operations in their queries. Developers familiar with JPQL syntax will find equivalent
object-level operations in the Criteria API.</p>

<p>The following simple Criteria query returns all instances of the <tt>Pet</tt> entity
in the data source:</p>

<pre>EntityManager em = ...;
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery&lt;Pet> cq = cb.createQuery(Pet.class);
Root&lt;Pet> pet = cq.from(Pet.class);
cq.select(pet);
TypedQuery&lt;Pet> q = em.createQuery(cq);
List&lt;Pet> allPets = q.getResultList();</pre><p>The equivalent JPQL query is:</p>

<pre>SELECT p
FROM Pet p</pre><p>This query demonstrates the basic steps to create a Criteria query:</p>


<ol><li><p>Use an <tt>EntityManager</tt> instance to create a <tt>CriteriaBuilder</tt> object.</p>

</li>
<li><p>Create a query object by creating an instance of the <tt>CriteriaQuery</tt> interface. This query object's attributes will be modified with the details of the query.</p>

</li>
<li><p>Set the query root by calling the <tt>from</tt> method on the <tt>CriteriaQuery</tt> object.</p>

</li>
<li><p>Specify what the type of the query result will be by calling the <tt>select</tt> method of the <tt>CriteriaQuery</tt> object.</p>

</li>
<li><p>Prepare the query for execution by creating a <tt>TypedQuery&lt;T></tt> instance, specifying the type of the query result.</p>

</li>
<li><p>Execute the query by calling the <tt>getResultList</tt> method on the <tt>TypedQuery&lt;T></tt> object. Because this query returns a collection of entities, the result is stored in a <tt>List</tt>.</p>

</li></ol>
<p>The tasks associated with each step are discussed in detail in this chapter.</p>

<p>To create a <tt>CriteriaBuilder</tt> instance, call the <tt>getCriteriaBuilder</tt> method on the <tt>EntityManager</tt> instance:</p>

<pre>CriteriaBuilder cb = em.getCriteriaBuilder();</pre><p>The query object is created by using the <tt>CriteriaBuilder</tt> instance:</p>

<pre>CriteriaQuery&lt;Pet> cq = cb.createQuery(Pet.class);</pre><p>The query will return instances of the <tt>Pet</tt> entity, so the type of
the query is specified when the <tt>CriteriaQuery</tt> object is created to create a
typesafe query.</p>

<p>The <tt>FROM</tt> clause of the query is set, and the root of the
query specified, by calling the <tt>from</tt> method of the query object:</p>

<pre>Root&lt;Pet> pet = cq.from(Pet.class);</pre><p>The <tt>SELECT</tt> clause of the query is set by calling the <tt>select</tt> method
of the query object and passing in the query root:</p>

<pre>cq.select(pet);</pre><p>The query object is now used to create a <tt>TypedQuery&lt;T></tt> object that can
be executed against the data source. The modifications to the query object are
captured to create a ready-to-execute query:</p>

<pre>TypedQuery&lt;Pet> q = em.createQuery(cq);</pre><p>This typed query object is executed by calling its <tt>getResultList</tt> method, because
this query will return multiple entity instances. The results are stored in a
<tt>List&lt;Pet></tt> collection-valued object.</p>

<pre>List&lt;Pet> allPets = q.getResultList();</pre>
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